In 3rd generation mobile communication, not only voice, but also video and data can be transmitted and received. The 3rd mobile communication is required to have a higher bandwidth because data traffic suddenly increases.
A task for constructing a network evolved to have a network having a higher bandwidth as described above (Long-Term Evolution Network: LTE) is in progress.
In the LTE, terms: an Evolved-UMTS (E-UMTS) and an Evolved-UTRAN (E-UTRAN) are used. In the E-UTRAN, Orthogonal Frequency Division Multiple Access (OFDMA) is used as Radio Access Technology (RAT).
FIG. 1 shows a wireless communication system.
The wireless communication system 10 includes one or more Base Stations (BSs) 11. The BS 11 commonly refers to a fixed station that communicates with User Equipments (UEs) 12, and it may also be called another terminology, such as an evolved-NodeB (eNB), a Base Transceiver System (BTS), or an access point. The BSs 11 provide communication services to respective geographical areas (commonly called cells) 15a, 15b, and 15c. The cell may be divided into a plurality of areas (called sectors). The UE 12 may be fixed or mobile and may also be called another terminology, such as a Mobile Station (MS), a Mobile Terminal (MT), a User Terminal (UT), a Subscriber Station (SS), a wireless device, a Personal Digital Assistant (PDA), a wireless modem, or a handheld device.
Downlink refers to communication from a BS to UE, and uplink refers to communication from UE to a BS. In downlink, a transmitter may be part of a BS, and a receiver may be part of UE. In uplink, a transmitter may be part of UE, and a receiver may be part of a BS.
LTE Physical Structure
3rd Generation Project Partnership (3GPP) Long Term Evolution (LTE) supports a radio frame structure of a type 1 which is applicable to Frequency Division Duplex (FDD) and a radio frame structure of a type 2 which is applicable to Time Division Duplex (TDD).
In a cellular OFDM wireless packet communication system, uplink/downlink data packet transmission is performed per subframe, and one subframe is defined as specific time duration including a number of Orthogonal Frequency Division Multiplexing (OFDM) symbols.
3GPP supports a type 1 radio frame structure applicable to Frequency Division Duplex (FDD) and a type 2 radio frame structure applicable to Time Division Duplex (TDD).
FIG. 2 shows the type 1 radio frame structure. The type 1 radio frame consists of 10 subframes, and one subframe consists of two slots.
FIG. 3 shows the type 2 radio frame structure. The type 2 radio frame consists of two half frames, and each of the two half frames includes 5 subframes, a Downlink Pilot Time Slot (DwPTS), a Gap Period (GP), and an Uplink Pilot Time Slot (UpPTS). From among them, one subframe includes two slots. The DwPTS is used for initial cell search, synchronization, or channel estimation in UE. The UpPTS is used for channel estimation in a BS and for the uplink transmission synchronization of UE. The GP is a period where interference occurring in uplink due to the multi-path delay of a downlink signal between uplink and downlink is removed. That is, one subframe consists of two slots irrespective of the type of radio frame.
FIG. 4 shows the slot structure of LTE downlink.
As shown in FIG. 4, a signal transmitted in each slot may be described by a resource grid that includes NRBDL NscRB subcarriers and NsymbDL Orthogonal Frequency Division Multiplexing (OFDM) symbols. Here, NRBDL indicates the number of Resource Blocks (RBs) in downlink, NscRB indicates the number of subcarriers that forms one RB, and NsymbDL indicates the number of OFDM symbols in one downlink slot.
FIG. 5 shows the slot structure of LTE uplink.
As shown in FIG. 5, a signal transmitted in each slot may be described by a resource grid that includes NRBDL NSCRB subcarriers and NsymbDL OFDM symbols. Here, NRBDL indicates the number of RBs in uplink, NscRB indicates the number of subcarriers that form one RB, and NsymbDL indicates the number of OFDM symbols in one downlink slot.
A resource element is a resource unit that is defined by an index (k, l) within an uplink slot and a downlink slot, and it indicates one subcarrier and one OFDM symbol. Here, k is an index on a frequency axis, and l is an index on a time axis.
LTE-Advanced
Meanwhile, there is a discussion on the development of a system which has been more advanced from LTE and is capable of providing a higher speed transmission/reception speed. In particular, the standardization task of International Mobile Telecommunication (IMT)-Advanced, that is, the next-generation mobile communication system, is in progress. An object of IMT-Advanced is to support multimedia service based on the Internet ProtoCol (IP) at a date rate of 1 Gbps in the stop and low-speed moving states and 500 Mbps in the high-speed moving state.
3rd Generation Partnership Project (3GPP) is a system standard which satisfies the requirements of IMT-Advanced and is preparing for LTE-Advanced (LTE-A) which is improved from Long Term Evolution (LTE) and is based on Orthogonal Frequency Division Multiple Access (OFDMA)/Single Carrier-Frequency Division Multiple Access (SC-FDMA) transmission methods. LTE-Advanced is one of powerful candidates for IMT-Advanced.
As described above, for higher data transmission and reception service, it is necessary to use a specific frequency band having an advantageous propagation characteristic. However, the development of new service and radio technology that use frequency bands is limited because the frequency bands are preoccupied by the existing radio service systems.
Accordingly, an LTE-Advanced (or also called LTE-A) system attempts to share the frequency bands with an LTE system. If the LTE-Advanced system shares the frequency bands with the LTE system, interference may occur between the LTE-Advanced system and the LTE system.
FIG. 6 is a diagram showing an example in which interference between systems occurs.
As can be seen from FIG. 6(a), the operating frequency bands of an LTE system and an LTE-A system may be disposed so that they are adjacent to each other.
As can be seen from FIG. 6(b), if an LTE-A system 15a sends a signal in this state, an adjacent LTE system 15b is subject to interference. Here, a system that gives the interference as described above is called an aggressor system (or a primary system), and a system that is subject to the interference is called a victim system (or a secondary system). Furthermore, UE in an aggressor system is called aggressor UE (or primary UE), and UE in a victim system is called victim UE (or secondary UE).
Here, a signal transmitted by the aggressor UE functions as interference to victim UE. A link between a BS and victim UE in the victim system is subject to interference, and this link is called a victim link.